We continued the development and application of label-fracture cytochemistry. With label-fracture, cells fixed or unfixed are labeled and then freeze-fractured. Label-fracture allows the observation - in a single, coincident image - the distribution of surface receptors and antigens superimposed on conventional Pt/C casts of freeze-fractured membranes. The resolution (5nm attainable) approaches the molecular level. This year we developed a new method for Label-Fracture: "Replica-Staining Label-Fracture". With this method we show that cytochemical labeling of cell surfaces can be performed by direct, post-fracture staining of freeze-fracture replicas. The new method for label-fracture leads to miniaturization of labeling procedures, allows standardization of labeling conditions and the simultaneous processing of different specimens. The work on localization of CD3 and CD4 antigens in human lymphocytes was continued using fracture-flip (see under Fracture-Flip. In other studies we used label-fracture to locate a glycoprotein related to the multi drug resistance of certain cell lines. We used a monoclonal antibody (MRK-16) in expressive and non-expressive fibroblast cell-lines to locate this glycoprotein (with Dr M. C. Willingham).